1. Technical Field
The present invention relates to an apparatus for inspecting defects of devices and a method of inspecting defects, in particular, to an apparatus for inspecting defects of devices useful for detecting defects of disconnection and short circuits of electric wiring and a method of inspecting defects.
2. Description of the Prior Art
A manufacturing process of a semiconductor is composed of iteration of serial processes such as exposure, etching, film forming and doping. Depending on maturity of a manufacturing process used, defect (form defects and electrical defects) inspection and dimension measurement are carried out between processes. From a viewpoint of early start-up of the manufacturing process, it is necessary to feed back the data from these inspection apparatuses and measuring apparatuses promptly to the manufacturing process. As for form inspection apparatuses for inspecting foreign particles on a device or abnormal forms thereof, there are optical microscopes and scanning electron microscopes. On the other hand, as for inspection apparatuses for electric defects such as disconnection and short circuits of wiring in a device, there are scanning electron microscopes (hereinafter referred to as xe2x80x9cSEMxe2x80x9d) and inspection apparatuses utilizing voltage contrasts in images from scanning ion microscopes (hereinafter referred to as xe2x80x9cSIMxe2x80x9d). The latter inspection apparatuses using an electron beam or a focused ion beam (hereinafter referred to as xe2x80x9cFIBxe2x80x9d) are disclosed, for example, in Japanese Patent Laid-Open Publications Hei 9 (1997)-326425, Hei 10 (1998)-313027 and Hei 11 (1999)-121559.
In a voltage contrast image, a voltage on a component forming the image determines luminance of the component in the image. Such voltage on the component may be applied thereto with a mechanical probe (a conductor probe) or by bestowment of electric charges from the scanning beam itself. In the latter case, since floating conductors (such as wiring) are charged slightly positive, they seem dark or drab in the case of observing SIM images with an optimized inspection apparatus. On the contrary, since electric charges are not stored in grounded conductors, they are observed as images of the same brightness. Moreover, in order to optimize detecting capability of voltage contrasts, also known is provision of filter mesh in which bias electric potential is applied between a sample and a secondary electron detector.
Either a conductor probe which is loaded on a sample stage and moves synchronously with the sample stage (hereinafter referred to as a xe2x80x9csample stage synchronous type conductor probexe2x80x9d), or a conductor probe which is fixed (to a ceiling face of a sample chamber, for example,) relatively with respect to an FIB generator (hereinafter referred to as a xe2x80x9cfixed type conductor probexe2x80x9d) is adopted as the conductor probe of a conventional inspection apparatus.
Although a chip size of a silicon integrated circuit changes along with its generation, the chip size of the current generation and the next generation is a square of about 20 to 25 mm, in the meantime, one unit size of a test element group (TEG) thereof is a square of about 1 to 2.5 mm, and a minimum width of wiring thereof is 0.1 to 0.5 xcexcm. Here, the TEG refers to a test element group for monitoring characteristic values and manufacturing processes of various elements such as transistors, capacitors, resistors and wiring. Meanwhile, in defect observation of TEG pattern wiring of 0.1 xcexcm level with a conventional FIB apparatus, for example, when 0.1 xcexcm is allotted to 4 pixels in an SIM image, then a visual field of a 1024xc3x971024 pixel SIM image is equivalent to a square of about 26 xcexcm. Such a size is {fraction (1/40)} to {fraction (1/200)} as small as one TEG unit size that is a square of 1 to 2.5 mm. However, operability will be improved if a visual field of an SIM image at a minimum magnification can almost cover a full range of the one TEG unit by combination of a beam shift function that shifts an original point of the visual filed of the SIM image. Nevertheless, even if coverage of the one TEG unit being the square of 1 to 2.5 mm is achieved, it is yet impossible to observe SIM images of circuit wiring patterns of all TEGs formed within one chip without moving the sample stage.
The conductor probe in the conventional inspection apparatus is either the sample stage synchronous type conductor probe that is loaded on the sample stage and moves synchronously with the sample stage, or the fixed type conductor probe that is relatively fixed with respect to the FIB generator. In general, there is a tendency that accuracies of moving positions become worse as a moving range of a tip of the conductor probe becomes wider. For this reason, a conductor probe that satisfies both wide-range moving across an entire surface of one chip (a square of about 20 to 25 mm) and high-accuracy moving positions within a visual filed of an SIM image at the minimum magnification (a square of 1 to 2.5 mm) had been yet to be found.
In consideration of the above-described problem of the prior art, an object of the present invention is to provide an apparatus for inspecting defects of devices that satisfies the demand for both wide-range moving and high-accuracy positioning moving within a narrow range and that improves usability of a conductor probe thereof for achieving higher inspection efficiency, and a method of inspecting defects.
According to the present invention, firstly, electric charges are supplied to a device (a semiconductor chip, for example) in such a manner that an electrically isolated component (wiring, for example) thereof has a different voltage from an electrically grounded component (a substrate, for example) thereof (Step 1). Next, voltage contrast data of the chip including the above-described components are obtained by use of an SIM image (Step 2). Lastly, any component showing a voltage different from a predetermined voltage with respect to such component is detected by analyzing the voltage contrast data (Step 3). In Step 1, supply of the electric charges occurs in the course of irradiating the FIB itself for SIM image observation, or a conductor probe using mechanical contact may be also used. Moreover, the conductor probe that effectuates mechanical contact with a floating conductor can remove the electric charges supplied by the FIB irradiation down to specified electric potential or additionally supply the electric charges. Thus, various control of the electric potential becomes feasible in comparison with the case using just the FIB, whereby high reliability upon defect inspection by the voltage contrast analysis is brought about. The conductor probe is combined with a conductor probe movement mechanism for moving the conductor probe, thus constituting conductor probe means.
An apparatus for inspecting defects of devices according to the present invention includes a plurality of conductor probe means, a part of which is conductor probe means of a movable type that moves synchronously with movement of a sample stage, and the remainder is conductor probe means of an immovable type that is relatively fixed with respect to a focused ion beam generator and does not move when the sample stage is moved.
Movement of visual field positions of SIM image observation is carried out only by beam shifting when a destination of the movement is located within an SIM image visual field of low magnification when an amount of beam shifting is set to zero (normally a square of several hundred micrometers). When the destination is located outside the visual field, the movement is carried out in a combination of large movement by the sample stage and fine movement by the beam shifting.
In an image display unit, besides an SIM observation image A of a sample surface, an inspection area image B that exhibits an inspection area of the sample is also displayed. Also, a visual field position of the SIM observation image A and tip positions of the conductor probes are superimposed on the inspection area image B. Moreover, display of the tip position of the conductor probes also bears status information as whether those probe tips are allowed to contact with the sample. When an operator wishes to move the observation visual field of the SIM observation image A or the tips of the conductor probes on the inspection area image B, provided is means for such operation by severally designating destinations. Furthermore, by linking a specific tip of a conductor probe with a central position of visual field of the SIM image, provided is link movement means where the tip of the conductor probe is allowed to move toward a position within a visual field of destination upon movement of such visual field of the SIM image.
Specifically, an apparatus for inspecting defects of devices according to the present invention is an apparatus for inspecting defects of devices including: a sample chamber; a movable sample stage for holding a device sample inside the sample chamber; a focused ion beam generator for irradiating a focused ion beam on the sample held on the sample stage; a charged particle detector for detecting secondary charged particles generated from the sample by irradiation of the focused ion beam; an image display unit for displaying an observation image A in which detected intensity of the secondary charged particles is converted into luminance signals; and a plurality of conductor probe means having conductor probes for contacting with the sample and conductor probe movement mechanisms for moving the conductor probes, wherein the conductor probe means includes: conductor probe means being fixed relatively with respect to the focused ion beam generator; and conductor probe means being fixed relatively with respect to the sample stage.
The conductor probe means fixed relatively with respect to the focused ion beam generator can move a tip of the conductor probe in higher positioning accuracy than the conductor probe means fixed relatively with respect to the sample stage. A moving range of the tip of the conductor probe is smaller in the conductor probe means fixed relatively with respect to the focused ion beam generator than in the conductor probe means fixed relatively with respect to the sample stage.
The conductor probe movement mechanism for the conductor probe means fixed relatively with respect to the focused ion beam generator can be fixed to a sidewall face of the sample chamber, a ceiling face thereof, or the focused ion beam generator. The conductor probe movement mechanism for the conductor probe means fixed relatively with respect to the sample stage can be fixed to the sample stage.
Moreover, it is preferable that the apparatus for inspecting defects of devices has a function of invariably locating the tip of the conductor probe of the conductor probe means fixed relatively with respect to the focused ion beam generator within a visual field of the observation image A.
It is preferable that the display unit displays an inspection area image B that indicates positions of the tips of the conductor probes on the sample. In this event, it is preferable that mechanical contact and non-contact of the tips of the conductor probes with the sample are also displayed in the inspection area image B. Moreover, a state of spatial interference among the plurality of conductor probes may be also displayed in the inspection area image B.
A method of inspecting defects in devices according to the present invention including the steps of allowing a tip of a conductor probe to contact with a point of voltage application on a device sample being held on a sample stage, irradiating a focused ion beam from a focused ion beam generator to the sample in a state that voltage is applied from the conductor probe to the sample, and detecting wiring defects based on voltage contrasts in an image taken with a scanning ion microscope by detecting secondary charged particles generated from the sample, which is characterized in that voltage application is carried out from the conductor probe held in a position fixed relatively with respect to the focused ion beam generator to a voltage application point of a sample necessary to be changed in relation with movement of a visual field of the scanning ion microscope, and that voltage application is carried out from the conductor probe held at the sample stage to a voltage application point of a sample not to be changed necessarily in relation with the movement of the visual field of the scanning ion microscope.
The movement of the visual field of the scanning ion microscope is carried out either by a sample stage movement or a beam shifting function. The voltage application point of the sample necessary to be changed in relation with the movement of the visual field of the scanning ion microscope refers generally to a voltage application point for confirmation of a defect, and it is typically set on fine patterns. The voltage application point of the sample not to be changed necessarily in relation with the movement of the visual field of the scanning ion microscope refers to a point for applying voltage on TEG patterns, such as a pad portion of wiring. The voltage application point in this case is not changed synchronously with the visual field of the scanning ion microscope during inspection of one TEG, however, it is necessary to change upon inspection of another TEG.
It is preferable that the tip of the conductor probe held in the position fixed relatively with respect to the focused ion beam generator is allowed to move as linked with the visual field of the scanning ion microscope.
Moreover, the position of the tip of the conductor probe can be displayed as a mark superimposed on a scanning ion microscopic image, and the displayed position of the mark can be moved relative to the scanning ion microscopic image so that the position of the tip of the conductor probe is moved corresponding to the movement. Such movement of the displayed position of the mark relevant to the scanning ion microscopic image can be performed by operating the mark by use of a pointing device such as a mouse.
According to the present invention, by the FIB scanning a device subject to inspection such as a semiconductor integrated circuit chip and applying desired electric potential while allowing the conductor probe to mechanically contact with an arbitrary position of a wiring portion on the chip, an SIM image of the chip is formed and defects such as disconnection or short circuits of the wiring can be detected with high reliability by analyzing electric potential contrasts thereof In particular, a plurality of the conductor probes are provided and at least one of them is a sample stage synchronous type conductor probe that is movable synchronously with the sample stage, while others are fixed type conductor probes being fixed relatively with respect to the focused ion beam generator. Accordingly, regarding one chip (a square of 20 to 25 mm) arranged with numerous TEGs (a square of 1 to 2.5 mm each), defects such as disconnection of wiring patterns in submicron sizes and short-circuit defects of the wiring patterns can be inspected over an entire region of the chip (regarding all the TEGs), with good operability, high efficiency and high reliability.